Principle and Application of Polarimetry

What is a polarimeter?

Polarimetry can be defined as the analysis of the rotation of polarized light by transparent components. Polarimetry is a responsive, non-destructive technique to measure the optical activity of organic and inorganic compounds. If linearly polarized light rotates when passing, it is assumed that a compound is optically active. The concentration of the chiral molecules and the molecular composition of the material determine the amount of optical rotation. The direction and extent of rotation are useful for qualitative and quantitative analysis and are also useful for the elucidation of chemical composition. Optical behavior is the ability to polarize light rotation in the determination of certain compounds.

Table of Contents What is a polarimeter? Principle of polarimeter Working principle of polarimeter Types of polarimeter Procedure of polarimeter Applications of polarimeter Advantages of polarimeter Disadvantages of polarimeter

Polarimeter principle:

The basic operation principle of a polarimeter includes a source that produces light with a specifically prepared linear polarization state, typically by going through a polarizer. The light is transmitted by an optically active sample that often rotates the polarization direction. After going through the sample, another measure of the changed angle of the polarization by transferring light through analyze, that can be rotated around the beam axis. The easiest technique is to move the analyzer to the place for which the transmission of optical power is at its lowest.

Working principle of polarimeter:

Polarimetry determines the rotation of polarized light as it travels through an optically active sample solution. A polarimeter includes a source of polarized light, filter, sample cell, analyzer, and a detector to measure the rotation angle. The determined rotation can be used to measure the concentrations of the sample particularly sugar, vitamins, peptides, and volatile oils.

Types of polarimeter:

Different types of polarimeters are mentioned below.

Manual polarimeter, fully-automatic, semi-automatic polarimeter, quartz-wedge polarimeter, biquartz polarimeter, lippich polarimeter, and Laurent’s half shade polarimeter, etc.

Polarimeter procedure:

Before beginning a polarimeter experiment, we must recognize the various components necessary to execute the process. The optical activity is calculated by the Polarimetry that consists of the source, filter, sample cell, analyzer, and detector.

Source: Sodium vapor lamps are usually used to produce wavelengths greater than 450 nm.

Filter: The filter is used to absorbing the undesired radiation of polychromatic light into monochromatic light.

Sample cell: Sample cells are used to place the sample in the sample compartment, there is made up of glass and has long tube-shaped.

Analyzer: It is mostly employed to analyze the samples when they rotate to the right or left side of the plane of polarized light.

Detector: The photomultiplier tube is broadly used for wavelength detection. The optically active component present in the solution rotates the plane-polarized light either in the clockwise direction or anti-clockwise direction. After that analyze calculates the angle of rotation and the detector detects it.

Experimental procedure of polarimeter:

• Prepare the sample solutions and standard solutions as you required.
• Switch the instrument to turn on and warm up for around 5 minutes.
• Rotate the Polaroid wheel so that display reads “ZERO”.
• Put the Polarimeter tube inside the instrument and close the cover.
• Rotate the wheel back and forth to display minimal intensity. Note down the readings of degrees (X1) and don’t disturb the system.
• Then take out the tube and refill it with the test solution, and put it back in its place. The intensity of the sample will rise due to the rotation of the plane of polarization.
• Rotate the wheel in the direction of decreasing intensity until the intensity reaches the minima and note down the readings of degrees (X2).

Polarimeter applications:

• Polarimetry is used to determine the specific rotation and optical rotation of products such as amino acids, cocaine, antibiotics, dextrose, carbohydrate, analgesics, vitamins, steroids, sugars, serums, diuretics, and codeine, etc.
• For structural determination, it can be used. In this application, changes in optical rotation about the substance chemical change are estimated.
• It is used to ensure product quality by determining the purity and concentration of compounds in sugar-based food, syrups, and cereals
• The applications of polarimeter consist, quantitative and qualitative analysis of optically active components.
• Polarimetry is used in the analysis of fragrance, flavor, and essential oil manufacturer
• Chiral compounds can also be determined by polarimetry.

Advantages of polarimeter:

• Polarimetry is an easy technique to operate and needs no experts to handle.
• It is not affected by changes in laser intensity.
• The temperature and pH within the eye remain stable.
• The advanced version of the polarimeter has a broad wavelength emission range over conventional light sources.
• The analysis is very easy and rapid, which means this a cost-effective technique.

Disadvantages of polarimeter:

• To determine the specific and optical rotation of a substance, it required large sample volumes with high concentrations.
• The major disadvantage of polarimetry is that the only optically active components can be analyzed by polarimetry.
• It has low sensitivity compared to other techniques.
• It is very sensitive to motion and scattering.

Commonly asked questions on polarimeter are as follows.

What is Polarimeter?

A polarimeter is an analytical tool that is used to determine the angle of rotation due to the passing of polarized light through the optically active molecule.

How does a polarimeter measure optical rotation?

A polarimeter is a tool that determines the angle of rotation bypassing the source of polarized light through the optically active material.

Which light source is used in the polarimeter?

Sodium (Na) vapor lamp is used in a polarimeter as a light source, since it produces monochromatic light and with high-energy output

What is the major advantage of a polarimeter?

The main advantage of a polarimeter is its analysis of a wide range of compounds.